Staggered-type Tunneling Field Effect Transistor

ABSTRACT

The disclosure describes a tunneling field effect transistor having an overlapping structure between the source and drain regions providing a greater tunneling area. The source or drain region may be a doped region in a semi-conductive substrate. The other source or drain region may be formed by epitaxial deposition over the doped region. The gate is formed over the epitaxial region where the doped and epitaxial regions overlap. The doped region may be formed in a fin structure with the epitaxial region and gate being formed on the top and sides of the fin.

BACKGROUND

The present application relates to the field of Tunneling Field EffectTransistors.

From the invention of the integrated circuit, it has been a goal to makethe devices on the integrated circuit smaller and smaller. This providesgreater functionality on each integrated circuit. However, with devicedimensions reaching the scale of tens of nanometers and operationalvoltages dropping to tenths of a volt, traditional MOSFETs have reachedsome physical limits. Thus, other transistor types are being explored.

One type of transistor is the Tunneling Field Effect Transistor (TFET).With this transistor, a tunneling region is modulated by a voltageapplied to a gate near the tunneling region. However, operationalcharacteristics of such devices in the art are not currently acceptablefor most commercial applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a process flow chart for fabricating a TFET, in accordancewith some embodiments;

FIGS. 2A-2D are side view diagrams illustrating the process of FIG. 1;

FIG. 3 is another process flow chart for fabricating a TFET, inaccordance with some embodiments;

FIGS. 4A-4D are side view diagrams illustrating the process of FIG. 3;

FIG. 5 is another process flow chart for fabricating a TFET, inaccordance with some embodiments;

FIGS. 6A-6D are side view diagrams illustrating the process of FIG. 5;

FIG. 7 is another process flow chart for fabricating a TFET, inaccordance with some embodiments;

FIGS. 8A-8D are side view diagrams illustrating the process of FIG. 7;

FIG. 9 is another process flow chart for fabricating a TFET, inaccordance with some embodiments;

FIGS. 10A-10D are side view diagrams illustrating a modification of theprocess of FIG. 7;

FIG. 11 is a process flow chart for fabricating a TFET, in accordancewith some embodiments;

FIGS. 12A-12I are side view diagrams illustrating a modification of theprocess of FIG. 11; and

FIG. 13 is a graph showing the performance characteristics of a TFET inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 is a flow chart showing a process flow according to someembodiments. FIGS. 2A-2D are side view diagrams illustrating the stepsof the process of FIG. 1. In step 101, a mask 14 is formed on thesurface of substrate 10 using conventional photolithographic techniques.An implantation of dopant ions 13 is then performed and then annealed toform source region 12. The substrate in this example is a crystallinesilicon substrate, but may be another semiconductor substrate such ascrystalline germanium or a III-V semiconductor. The dopant may be chosenfrom any known dopant atoms. In this example, source region 12 is dopedto a P++ doping level. For example, an implantation having an energy of20-40 KeV with a dose of 0.1 to 5×10¹⁵ atoms/cm² may be performed at atemperature of 1000° C. for about 10 seconds.

In step 103 and FIG. 2B, a thick oxide layer 16 is formed and patternedas shown in FIG. 2B. Oxide layer 16 may be formed using known chemicalvapor deposition techniques or thermally grown. With Oxide layer 16serving as a mask, drain region 18 is formed using epitaxial depositiontechniques, such as Chemical Vapor Deposition (CVD). In this example,drain region 18 is formed of SiGe and the relative concentrations ofsilicon and germanium are varied during deposition to create aheterojunction with source/drain 12. In some embodiments, drain region18 may be composed of Si, Ge, SiGe, SiC, GeSn, SiP or III-Vsemiconductor material. Source region 12 and drain region 18 aredesignated source and drain, respectively, in the embodiment of FIGS.2A-D. However, in other embodiments region 12 may serve as a drainregion and region 18 may serve as a source. That is, either region mayserve as a source or drain depending on selected doping and materialcomposition, and on the configuration of the circuit in which thetransistor is used.

In step 105 and FIG. 2C, a thick oxide layer 20 is formed and patternedas shown in FIG. 2C. In this example, oxide layer 20 is formed bychemical vapor deposition (CVD) techniques and is patterned usingstandard lithographic techniques. Next, in the opening between oxidelayers 16 and 20, a gate dielectric 22 is formed. Gate dielectric 22 isshown only in the bottom of the opening between oxide regions 16 and 20in FIG. 2C. However, in some embodiments, dielectric layer 22 may alsobe formed on the sides of oxide regions 16 and 20. In some embodiments,the gate dielectric layer 22 may include silicon oxide, silicon nitride,silicon oxy-nitride, or high dielectric constant (high-k) dielectric.High-k dielectrics comprise metal oxides. Examples of metal oxides usedfor high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. In some embodiments, the gate dielectric layer 22 hasa thickness in the range of about 10 angstroms to about 30 angstroms. Inthis example, gate dielectric is a High K dielectric material that isformed using ALD.

Gate electrode 24 is then formed on gate dielectric 22. Gate electrode24 may be doped polycrystalline silicon or may comprises a metalselected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN,TaSiN, Mn, Zr, TiN, WN, TaN, and Ru or combinations thereof. In someembodiments, the gate electrode layer 24 has a thickness in the range ofabout 30 nm to about 60 nm. The gate electrode layer 24 may be formedusing a suitable process such as ALD, CVD, physical vapor deposition(PVD), plating, or combinations thereof.

In step 107 and FIG. 2D, source and drain contact openings are formed inoxide layers 16 and 20, respectively. Source contact 26 and draincontact 28 are formed therein. The openings are made using standardphotolithographic and etching techniques. In one example, source contact26 and drain contact 28 include a barrier layer to line the contactopenings and a conductive layer deposited afterwards to fill the contactopenings. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes. In some embodiments,the thickness of the conductive layer is in a range from about 100 nm toabout 200 nm.

After the contact openings are filled, a planarization process, such aschemical mechanical polishing (CMP) process, is performed to remove thebarrier layer and conductive layer outside contact openings to providethe planar structure shown in FIG. 2D.

FIG. 3 is another example process flow. FIGS. 4A-4D are side viewsillustrating the process of FIG. 3. Elements in common with the processof FIGS. 2A-2D bear the same identification number. In step 201, a mask14 is formed on the surface of substrate 10 using conventionalphotolithographic techniques. An implantation of dopant ions 13 is thenperformed and then annealed to form source region 12. The substrate inthis example is a crystalline silicon substrate. The dopant may bechosen from any known dopant atoms. In this example, source region 12 isdoped to a P++ doping level. For example, an implantation having anenergy of 20-40 KeV with a dose of 0.1 to 5×10¹⁵ atoms/cm² be performedat a temperature of 1000° C. for about 10 seconds.

In step 203 and FIG. 4B, a thick oxide layer 16 is formed and patternedas shown in FIG. 4B. Oxide layer 16 may be formed using known chemicalvapor deposition techniques or thermally grown. With oxide layer 16serving as a mask, a portion of substrate 10 is removed using commonetching techniques. The etch process may be reactive ion etch using SF6,SiCl4, C4F8, CH4, H2 or other known etch gases. It is preferred that theetch process parameters be selected to provide an etch that is asanisotropic as is practicable. In step 205, the drain region 18 then isformed using epitaxial deposition techniques, such as ALD. In thisexample, drain region 18 is formed of SiGe and the relativeconcentrations of silicon and germanium are varied during deposition tocreate a heterojunction with source 12. In some embodiments, drainregion 18 may be composed of Si, Ge, SiGe, SiC, GeSn, SiP or III-Vsemiconductor material. By etching the substrate 10, the top of drainregion 18 is then roughly even with the top of substrate 10. Thisrelative planarity aids in subsequent production steps.

In step 207 and FIG. 4C, a thick oxide layer 20 is formed and patternedas shown in FIG. 4C. In this example, oxide layer 20 is formed bychemical vapor deposition (CVD) techniques and is patterned usingstandard lithographic techniques. Next, in the opening between oxidelayers 16 and 20, a gate dielectric 22 is formed. In some embodiments,the gate dielectric layer 22 may include silicon oxide, silicon nitride,silicon oxy-nitride, or high dielectric constant (high-k) dielectric.High-k dielectrics comprise metal oxides. Examples of metal oxides usedfor high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. In some embodiments, the gate dielectric layer 22 hasa thickness in the range of about 10 angstroms to about 30 angstroms. Inthis example, gate dielectric is a High K dielectric material that isformed using ALD.

Gate electrode 24 is then formed on gate dielectric 22. Gate electrode24 may be doped polycrystalline silicon or may comprise a metal selectedfrom a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn,Zr, TiN, WN, TaN, and Ru or combinations thereof. In some embodiments,the gate electrode layer 24 has a thickness in the range of about 30 nmto about 60 nm. The gate electrode layer 24 may be formed using asuitable process such as ALD, CVD, PVD, plating, or combinationsthereof.

In step 209 and FIG. 4D, source and drain contact openings are formed inoxide layers 16 and 20, respectively. Source contact 26 and draincontact 28 are formed therein. The openings are made using standardphotolithographic and etching techniques. In one example, source contact26 and drain contact 28 include a barrier layer to line the contactopenings and a conductive layer deposited afterwards to fill the contactopenings. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of a diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes. In some embodiments,the thickness of the conductive layer is in a range from about 100 nm toabout 200 nm.

After the contact openings are filled, a planarization process, such aschemical mechanical polishing (CMP), is performed to remove the barrierlayer and conductive layer outside contact openings to provide theplanar structure shown in FIG. 4D.

FIG. 5 is another example process flow. FIGS. 6A-6D are side viewsillustrating the process of FIG. 5. Elements in common with the processof FIGS. 4A-4D bear the same identification number. In step 301, a mask14 is formed on the surface of substrate 10 using conventionalphotolithographic techniques. In addition, a sidewall spacer 15 isformed by depositing a layer and etching the layer anisotropically usinga process such as RIE. The composition of the layer is not critical asthe sidewall spacer 15 is subsequently removed. Exemplary materials maybe silicon dioxide, silicon nitride or polyimide. An implantation ofdopant ions 13 is then performed and then annealed to form source region12. The substrate in this example is a crystalline silicon substrate.The dopant may be chosen from any known dopant atoms. In this example,source region 12 is doped to a P++ doping level. For example, animplantation having an energy of 20-40 KeV with a dose of 0.1 to 5×10¹⁵atoms/cm² may be performed at a temperature of 1000° C. for about 10seconds.

In step 303 and FIG. 6B, a thick oxide layer 16 is formed and patternedas shown in FIG. 6B. Oxide layer 16 may be formed using known chemicalvapor deposition techniques or thermally grown. With Oxide layer 16serving as a mask, drain region 18 then is formed using epitaxialdeposition techniques, such as ALD. In this example, drain region 18 isformed of SiGe and the relative concentrations of silicon and germaniumare varied during deposition to create a heterojunction with source 12.In some embodiments, drain region 18 may be composed of Si, Ge, SiGe,SiC, SiP or III-V semiconductor material.

In step 305 and FIG. 6C, a thick oxide layer 20 is formed and patternedas shown in FIG. 6C. In this example, oxide layer 20 is formed bychemical vapor deposition (CVD) techniques and is patterned usingstandard lithographic techniques. Next, in the opening between oxidelayers 16 and 20, a gate dielectric 22 is formed. In some embodiments,the gate dielectric layer 22 may include silicon oxide, silicon nitride,silicon oxy-nitride, or high dielectric constant (high-k) dielectric.High-k dielectrics comprise metal oxides. Examples of metal oxides usedfor high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. Gate oxide layer 22 is shown only in the bottom of thegap between oxide layers 16 and 20 in FIG. 6C. However, gate oxide layermay also extend to the sides of oxide layers 16 and 20. In someembodiments, the gate dielectric layer 22 has a thickness in the rangeof about 10 angstroms to about 30 angstroms. In this example, gatedielectric is a High K dielectric material that is formed using atomiclayer deposition (ALD).

Gate electrode 24 is then formed on gate dielectric 22. Gate electrode24 may be doped polycrystalline silicon or may comprises a metalselected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN,TaSiN, Mn, Zr, TiN, WN, TaN, and Ru or combinations thereof. In someembodiments, the gate electrode layer 24 has a thickness in the range ofabout 30 nm to about 60 nm. The gate electrode layer 24 may be formedusing a suitable process such as ALD, CVD, PVD, plating, or combinationsthereof.

In step 307 and FIG. 6D, source and drain contact openings are formed inoxide layers 16 and 20, respectively. Source contact 26 and draincontact 28 are formed therein. The openings are made using standardphotolithographic and etching techniques. In one example, source contact26 and drain contact 28 include a barrier layer to line the contactopenings and a conductive layer deposited afterwards to fill the contactopenings. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes. In some embodiments,the thickness of the conductive layer is in a range from about 100 nm toabout 200 nm.

After the contact openings are filled, a planarization process, such asa CMP, is performed to remove the barrier layer and conductive layeroutside contact openings to provide the planar structure shown in FIG.6D. By offsetting source 12 from the edge of gate 24, a more uniformelectric field is applied to all of the junction between the source 12and drain 18, thus providing better tunneling behavior in response to anapplied gate voltage.

FIG. 7 is another example process flow. FIGS. 8A-D are side viewsillustrating the process of FIG. 7. Elements in common with the processof FIGS. 6A-6D bear the same identification number. In step 401, a mask14 is formed on the surface of substrate 10 using conventionalphotolithographic techniques. In addition, a sidewall spacer 15 isformed by depositing a layer and etching the layer anisotropically usinga process such as RIE. An implantation of dopant ions 13 is thenperformed and then annealed to form source region 12. The substrate inthis example is a crystalline silicon substrate. The dopant may bechosen from any known dopant atoms. In this example, source region 12 isdoped to a P++ doping level. For example, an implantation having anenergy of 20-40 KeV with a dose of 0.1 to 5×10¹⁵ atoms/cm² be performedat a temperature of 1000° C. for about 10 seconds.

In step 403 and FIG. 8B, a thick oxide layer 16 is formed and patternedas shown in FIG. 8B. Oxide layer 16 may be formed using known chemicalvapor deposition techniques or thermally grown. Sidewall spacer 17 isformed by depositing a layer of, for example, silicon dioxide depositedusing CVD and then anisotropically etching the deposited layer. WithOxide layer 16 and sidewall spacer 17 serving as a mask, drain region 18then is formed using epitaxial deposition techniques, such as ALD. Inthis example, drain region 18 is formed of SiGe and the relativeconcentrations of silicon and germanium are varied during deposition tocreate a heterojunction with source 12. In some embodiments, drainregion 18 may be composed of Si, Ge, SiGe, SiC, GeSn, SiP or III-Vsemiconductor material.

In step 405 and FIG. 8C, a thick oxide layer 20 is formed and patternedas shown in FIG. 8C. In this example, oxide layer 20 is formed bychemical vapor deposition (CVD) techniques and is patterned usingstandard lithographic techniques. Next, in the opening between oxidelayers 16 and 20, a gate dielectric 22 is formed. In some embodiments,the gate dielectric layer 22 may include silicon oxide, silicon nitride,silicon oxy-nitride, or high dielectric constant (high-k) dielectric.High-k dielectrics comprise metal oxides. Examples of metal oxides usedfor high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. In some embodiments, the gate dielectric layer 22 hasa thickness in the range of about 10 angstroms to about 30 angstroms. Inthis example, gate dielectric is a High K dielectric material that isformed using atomic layer deposition (ALD).

Gate electrode 24 is then formed on gate dielectric 22. Gate electrode24 may be doped polycrystalline silicon or may comprises a metalselected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN,TaSiN, Mn, Zr, TiN, WN, TaN, and Ru or combinations thereof. In someembodiments, the gate electrode layer 24 has a thickness in the range ofabout 30 nm to about 60 nm. The gate electrode layer 24 may be formedusing a suitable process such as ALD, CVD, physical vapor deposition(PVD), plating, or combinations thereof. Because gate electrode 24extends beyond the tunneling interface area between source region 12 anddrain region 18, a more uniform electric field can be applied to thistunneling interface, thus improving performance.

In step 407 and FIG. 8D, source and drain contact openings are formed inoxide layers 16 and 20, respectively. Source contact 26 and draincontact 28 are formed therein. The openings are made using standardphotolithographic and etching techniques. In one example, source contact26 and drain contact 28 include a barrier layer to line the contactopenings and a conductive layer deposited afterwards to fill the contactopenings. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes. In some embodiments,the thickness of the conductive layer is in a range from about 100 nm toabout 200 nm.

After the contact openings are filled, a planarization process, such asCMP, is performed to remove the barrier layer and conductive layeroutside contact openings to provide the planar structure shown in FIG.8D. By offsetting source 12 and drain 18 from the edge of gate 24, amore uniform electric field is applied to all of the tunneling junctionbetween the source 12 and drain 18, thus providing better tunnelingbehavior in response to an applied gate voltage.

FIG. 9 is another example process flow. FIGS. 10A-D are side viewsillustrating the process of FIG. 9. Elements in common with the processof FIGS. 8A-8D bear the same identification number In step 451, a mask14 is formed on the surface of substrate 10 using conventionalphotolithographic techniques. In addition, a sidewall spacer 15 isformed by depositing a layer and etching the layer anisotropically usinga process such as RIE. An implantation of dopant ions 13 is thenperformed and then annealed to form source region 12. The substrate inthis example is a crystalline silicon substrate. The dopant may bechosen from any known dopant atoms. In this example, source region 12 isdoped to a P++ doping level. For example, an implantation having anenergy of 20-40 KeV with a dose of 0.1 to 5×10¹⁵ atoms/cm² be performedat a temperature of 1000° C. for about 10 seconds.

In step 453 and FIG. 10B, a thick oxide layer 16 is formed and patternedas shown in FIG. 10B. Oxide layer 16 may be formed using known chemicalvapor deposition techniques or thermally grown. In addition, a sidewallspacer 17 is formed by depositing a layer and etching the layeranisotropically using a process such as RIE. With Oxide layer 16 andsidewall spacer 17 serving as a mask, drain region 18 then is formedusing epitaxial deposition techniques, such as ALD. In this example,drain region 18 is formed of SiGe and the relative concentrations ofsilicon and germanium are varied during deposition to create aheterojunction with source 12. In some embodiments, drain region 18 maybe composed of Si, Ge, SiGe, SiC, SiP or III-V semiconductor material.

In step 455 and FIG. 10C, a thick oxide layer 20 is formed and patternedas shown in FIG. 10C. In this example, oxide layer 20 is formed bychemical vapor deposition (CVD) techniques and is patterned usingstandard lithographic techniques. Next, in the opening between oxidelayers 16 and 20, a gate dielectric 22 is formed. In some embodiments,the gate dielectric layer 22 may include silicon oxide, silicon nitride,silicon oxy-nitride, or high dielectric constant (high-k) dielectric.High-k dielectrics comprise metal oxides. Examples of metal oxides usedfor high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. In some embodiments, the gate dielectric layer 22 hasa thickness in the range of about 10 angstroms to about 30 angstroms. Inthis example, gate dielectric is a High K dielectric material that isformed using atomic layer deposition (ALD).

Gate electrode 24 is then formed on gate dielectric 22. Gate electrode24 may be doped polycrystalline silicon or may comprises a metalselected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN,TaSiN, Mn, Zr, TiN, WN, TaN, and Ru or combinations thereof. In someembodiments, the gate electrode layer 24 has a thickness in the range ofabout 30 nm to about 60 nm. The gate electrode layer 24 may be formedusing a suitable process such as ALD, CVD, physical vapor deposition(PVD), plating, or combinations thereof.

In step 457 and FIG. 10D, source and drain contact openings are formedin oxide layers 16 and 20, respectively. Source contact 26 and draincontact 28 are formed therein. The openings are made using standardphotolithographic and etching techniques. In one example, source contact26 and drain contact 28 include a barrier layer to line the contactopenings and a conductive layer deposited afterwards to fill the contactopenings. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes. In some embodiments,the thickness of the conductive layer is in a range from about 100 nm toabout 200 nm.

After the contact openings are filled, a planarization process, such asCMP, is performed to remove the barrier layer and conductive layeroutside contact openings to provide the planar structure shown in FIG.8D. By offsetting source 12 and drain 18 from the edge of gate 24, amore uniform electric field is applied to all of the tunneling junctionbetween the source 12 and drain 18, thus providing better tunnelingbehavior in response to an applied gate voltage.

FIG. 11 is a process flow for TFET having a fin-shaped structure, whichis an example. FIGS. 12A-12H are side views of the process shown in FIG.11. In step 501 and FIG. 12A, a sacrificial oxide 102 is grown on thesurface of substrate 100, which, in this example, is a crystallinesilicon substrate. A masking layer 106 is then deposited and patternedusing standard photolithographic techniques. Using the masking layer106, an implantation 108 is performed to form source region 111 as shownin FIG. 12B. The dopant may be chosen from any known dopant atoms. Inthis example, source region 12 is doped to a P++ doping level. Forexample, an implantation having an energy of 20-40 KeV with a dose of0.1 to 5×10¹⁵ atoms/cm² be performed at a temperature of 1000° C. forabout 10 seconds. Masking layer 106 is then removed.

In step 503 shown in FIG. 12B, a thick oxide 110 is formed on thesurface of substrate 100. Oxide layer 110 is, for example, formed to athickness of 100 nm using, for example, plasma enhanced chemical vapordeposition (PECVD). In step 505, thick oxide 110 is then patterned asshown in FIG. 12C. The central part of the pattern defines where the finwill be, and is, for example 100-150 nm long and 50-70 nm wide. In step507, using patterned thick oxide layer 110 as a mask, openings 112 areetched into substrate 100 using, for example, RIE.

In step 509, isolation oxide regions 114 are formed in the bottoms ofopenings 112 as shown in FIG. 12E using conventional techniques forforming shallow trench isolation. The top of isolation oxide regions 114is below the top of drain layer 118 to allow the gate stack 120(described below) to modulate as much of the source/drain tunnelinginterface as possible, thus maximizing the source to drain current.Then, oxide layer 110 is patterned and etched so that a portion of oxidelayer 110 over what will be the gate and drain regions is removedleaving a cap 116 as shown in FIG. 12F on a portion of the source region111 where a contact will be formed.

In step 511, a selective epitaxial growth process such as ALD is used toform a drain layer 118 on the exposed surfaces of substrate 110 as shownin FIG. 12G. In this example, drain layer 118 comprises SiGe and therelative concentrations of Si and Ge are varied during deposition toprovide a heterojunction with the source area. Drain layer 118 can be 3to 10 nm thick. The cap 116 is then removed using conventional etchingtechniques. In step 515, a gate stack 120 is then formed and patternedas shown in FIG. 12H. To form gate stack 120, a high-K gate dielectricis first deposited using ALD to a thickness of 10 to 30 Å. High-kdielectric materials include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr,Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu andmixtures thereof. The conductive gate is then formed by ALD. Theconductive gate may be doped polycrystalline silicon or may comprises ametal selected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC,TaCN, TaSiN, Mn, Zr, TiN, WN, TaN, and Ru or combinations thereof. Insome embodiments, the conductive gate has a thickness in the range ofabout 30 nm to about 60 nm.

In step 517, source contact 122 and drain contact 124 are deposited andpatterned on the source region 111 and drain region 118, respectively,as shown in FIG. 12I. In one example, source contact 122 and draincontact 124 include a barrier layer and a conductive layer depositedafterwards. The barrier layer may promote adhesion of the conductivelayer. In addition, if the conductive layer is made of diffusiveelement, such as Cu, the barrier layer blocks diffusion into neighboringlayers or structures. In some embodiments, the barrier layer includesTi, TiN, Ta, TaN, or combinations thereof. The barrier layer may beformed by PVD, ALD, or other applicable processes. In some embodiments,the thickness of layer is in a range from about 1 nm to about 10 nm.

The conductive layer may be made of any conductive metal or metal alloy.Examples of suitable conductive metals include, but are not limited to,Cu, Al, W, Pt, Au, Ag, etc. The conductive layer may be formed byplating, PVD, ALD, or other applicable processes.

FIG. 13 is a graph showing the improved performance of the forgoingexamples relative to conventional TFETs. Line 300 shows the subthresholdperformance of conventional TFETs (the left-hand side of the graph isp-type and the right-hand side is n-type). Line 400 shows theperformance of an overlapping or staggered TFET according to the aboveexamples with a simple PN type tunneling barrier. This shows anapproximate fivefold increase in drive current over conventional TFETs.Line 500 shows a TFET according to the above examples where the drain isformed using SiGe on a silicon substrate. This shows an approximateseventeen-fold increase in drive current over conventional TFETs. Line600 shows a TFET according to the above examples with a SiGe drain on asilicon substrate with a heterojunction profile at the transition fromSiGe to silicon. As can be seen, this provides a drive current increaseof approximately four orders of magnitude over conventional TFETs.

The above examples show structures for and processes for fabricating astaggered or overlapping structure tunneling field effect transistor.The process is compatible with current CMOS manufacturing techniques,thus minimizing the cost for incorporating this new transistor intocurrent production facilities. More importantly, applying the techniquestaught in this specification can provide a TFET with drive current fourorders of magnitude greater than conventional TFETs. This greater drivecurrent along with a low subthreshold swing (FIG. 13) and low thresholdvoltage makes the examples described herein attractive for use inhigh-density, low-power integrated circuits.

A tunneling field effect transistor is described including a dopedregion formed in a semi-conductive substrate. An epitaxial region isformed overlapping the doped region in an overlapping region. A gate isformed adjacent to the overlapping region. The doped region serves as adrain and the epitaxial region serves as the source of the tunnelingfield effect transistor.

A tunneling field effect transistor is described including a dopedregion formed in a crystalline silicon substrate. A silicon-germaniumepitaxial region is formed overlapping the doped region in anoverlapping region. A gate is formed adjacent to the overlapping region.The doped region serves as a drain and the epitaxial region serves asthe source of the tunneling field effect transistor.

A method for forming a tunneling field effect transistor is describedincluding forming a doped region formed in a semi-conductive substrate.An epitaxial region overlapping the doped region is deposited to form anoverlapping region. A gate is formed adjacent to the overlapping region.The doped region serves as a drain and the epitaxial region serves asthe source of the tunneling field effect transistor.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A tunneling field effect transistor comprising: adoped region formed in a semi-conductive substrate; an epitaxial regionformed overlapping the doped region in an overlapping region; and a gateformed adjacent to the overlapping region; wherein the doped regionserves as a source or drain and the epitaxial region serves as a sourceor drain of the tunneling field effect transistor.
 2. A tunneling fieldeffect transistor as in claim 1 wherein the epitaxial region is acompound semiconductor.
 3. A tunneling field effect transistor as inclaim 1 further comprising a gate insulator interposed between the gateand the overlapping region.
 4. A tunneling field effect transistor as inclaim 1 wherein the gate overlies the epitaxial region and the dopedregion is underneath the epitaxial region.
 5. A tunneling field effecttransistor as in claim 1 wherein the epitaxial region is formed in adepression etched from the surface of the substrate.
 6. A tunnelingfield effect transistor as in claim 1 wherein the doped region is formedin a fin-shaped structure on the surface of the substrate, the epitaxialregion is formed over the top and sides of the fin-shaped structure andthe gate is formed over the top and sides of the epitaxial region.
 7. Atunneling field effect transistor comprising: a doped region formed in acrystalline silicon substrate; a silicon-germanium epitaxial regionformed overlapping the doped region in an overlapping region; and a gateformed adjacent to the overlapping region; wherein the doped regionserves as a source or drain and the epitaxial region serves as a sourceor drain of the tunneling field effect transistor.
 8. A tunneling fieldeffect transistor as in claim 7 wherein the interface between the dopedregion and the epitaxial region is a heterojunction.
 9. A tunnelingfield effect transistor as in claim 7 further comprising a gateinsulator interposed between the gate and the overlapping region.
 10. Atunneling field effect transistor as in claim 7 wherein the gateoverlies the epitaxial region and the doped region is underneath theepitaxial region.
 11. A tunneling field effect transistor as in claim 7wherein the epitaxial region is formed in a depression in the surface ofthe substrate.
 12. A tunneling field effect transistor as in claim 7wherein the doped region is formed in a fin-shaped structure on thesurface of the substrate, the epitaxial region is formed over the topand sides of the fin-shaped structure and the gate is formed over thetop and sides of the epitaxial region.
 13. A method for forming atunneling field effect transistor comprising: forming a doped regionformed in a semi-conductive substrate; depositing an epitaxial regionoverlapping the doped region to form an overlapping region; and forminga gate adjacent to the overlapping region; wherein the doped regionserves as a source or drain and the epitaxial region serves as a sourceor drain of the tunneling field effect transistor.
 14. The method ofclaim 13 wherein the doped region is formed by implantation of ions intothe substrate.
 15. The method of claim 13 further comprising forming agate insulator on the epitaxial region before forming the gate.
 16. Themethod of claim 15 wherein the gate insulator comprises a high Kdielectric material.
 17. The method of claim 13 wherein the dopingprofile of the doped region is and the composition of the epitaxialregion are controlled to provide a heterojunction between the dopedregion and the epitaxial region.
 18. The method of claim 13 furthercomprising forming a fin-shaped structure in the substrate wherein thedoped region is formed in the fin-shaped structure; the epitaxial regionis formed on the top and sides of the fin-shaped structure and the gateis formed on the top and sides of the epitaxial region.
 19. The methodof claim 13 wherein the substrate comprises crystalline silicon and theepitaxial region comprises silicon-germanium.
 20. The method of claim 13wherein the doped region is laterally spaced from a first end of thegate and the epitaxial region is laterally spaced form a second end ofthe gate.